In a stereo slide photographed by a stereo camera in which the interval between the optical axes of the right and left lenses is fixed, non-overlapping portions, in which the photographic ranges of the right and left photographic pictures are not brought into agreement with each other, are formed due to a difference in the visual field of the right and left photographic lenses of the stereo camera. These non-overlapping portions do not contribute to forming a solid image when the slides are viewed by using a stereo slide viewer. When a stereo slide in which the non-overlapping portions are not masked is viewed by two eyes, the edges of the other windows appear as vertical lines along the boundaries between the overlapping portions and the non-overlapping portions to impair taste or visual appearance. Accordingly, to prevent this, the windows of the stereo slide mount have been formed in a width narrower than the size of the picture of the slide films so as to mask the non-overlapping portions.
The width of the non-overlapping portions to be masked increases as the photographing distance to a subject which most influences matching of the right and left pictures approaches. Therefore, there have been provided plural kinds of stereo slide mounts having stepwisely different widths of windows. The stereo slide mount having a window of a suitable width for masking is selected from these stereo slide mounts to mount the slide film. However, it is not easy to judge the amount of masking required by viewing a pair of slide films after each frame is cut, and the problem arises that a stereo slide mount is frequently erroneously selected.
In obtaining a suitable stereo effect in the stereo slide, it is known that a subject which most influences matching of right and left images should be disposed in the same position relative to the right and left windows of the stereo slide mount. If the positions of the subject are different on the right and left, the natural stereo effect is impaired. However, a conventional stereo slide mount does not have any means of positioning the film in the right-to-left direction and it has the disadvantage that it is not easy to position the film in a suitable position.
The present applicant has previously proposed a stereo slide system in which a stereo slide photographed by a stereo camera having a predetermined positional relationship between the perforations of a film and a photographing picture is mounted on a stereo slide mount using a picture masking amount guide device/stereo slide viewer, to eliminate at least some of the disadvantages of a conventional stereo slide system (Japanese Patent Application No. 8-029177).
The stereo slide mount of such a stereo slide system is made up of a base frame which is provided with film positioning pins around the edges of both right and left windows, and a cover frame selected from several possible cover frames in which the gap widths between right and left windows are the same and the widths of the windows are stepwisely different. The picture masking-amount guide device/stereo slide viewer can be used to choose a suitable masking amount by observing a solid image while varying the masking amount of the outer region of the picture of the stereo slide. After the masking amount is determined, the perforations of the film are engaged with the positioning pins of the base frame to position the film. Next the cover frame having the width of the window corresponding to the determined masking amount is selected, and joined to the base frame. Then, the film is positioned at a predetermined position, and the non-overlapping portions of the outer side of the right and left films are masked to obtain an accurate stereo effect.
The above-mentioned stereo slide mount can be accurately and easily positioned at the time of mounting as described above, but since the cover frames having different width windows have the same gap widths between the right and left windows, the pitch at the center between the right and left pictures is narrowed as the width of the windows is narrowed, and hence the optical angles of the two eyes become different depending upon the pitch of the pictures.
The change of the pitch of the right and left pictures is not always such a large problem when viewing stereo slides, but when various stereo slides having large differences of pitch of picture are frequently changed and viewed for a long time, the adaption of the eyes for the change of the optical angle slows down and the person viewing the stereo slides can feel discomfort or fatigue.
In order to easily mount and accurately position the stereo slide and to provide a stereo slide mount which allows easy viewing without causing fatigue, it becomes necessary to solve this technical problem. The object of the present invention is to address this technical problem.